A protease is a critical factor involved in neoplastic disorders and cancer and thus it gets importance more than ever. Cell growth, angiogenesis, invasion, migration, metastasis, survival, expansion and progression of tumor cells depend on proteolytic activities and cell signaling regulation of a protease. For example, the unregulated protease is characteristically involved in degradation and remodeling of an extracellular matrix forming an intercellular space matrix and the basement membrane, by which tumor cells are permeated into nearby tissues locally and further transferred to remote areas. Invasion and metastasis of tumor cells are very important indexes to predict and determine the prognosis of cancer. Therefore, a gene involved in regulation of metastasis can be not only used as a prognostic marker but also be an important target for cancer therapy. The representative metastasis related genes are MMPs (matrix metalloproteinases), cathepsin B, cathepsin D and uPA (urokinase plasminogen activator) containing serine protease (DeClerck; Y. A. and Imeren, S. Eur. J. Cancer 30A(14):2170-2180, 1994).
In particular, the functions of MMPs in relation to tumor invasion and metastasis have been best known. MMPs are members of zinc-dependent endopeptidase according to their structures, which are over-expressed in tumor microenvironment and able to decompose almost every extracellular matrix protein components. MMPs play a key role not only in cancer progression, that is invasion into the basement membrane and stroma, infiltration into blood vessel, metastasis, etc, but also in cell proliferation, growth factor release and cell migration as well (Stetler-Stevenson, W. G., Yu, A. E. Semin. Cancer Biol. 11(2):143-152, 2001). MMP has been reported to be over-expressed in tissues of various tumors such as breast cancer, prostatic carcinoma, ovarian cancer, lung cancer, large intestine cancer, and pancreas cancer. The high expressions of various MMP family members have been confirmed to be closely related to tumor aggressiveness (Nelson, A. R., et al., J. Clin. Oncol. 18(5):1135-1149, 2000). For example, MMP-1 and MMP-7 are the potential prognostic factors for large intestine cancer. Some MMP inhibitors have been proved to have metastasis inhibiting effect in pre-clinical phase and clinical phase.
It was also reported that the high expressions of uPA and uPAR (urokinase plasminogen activator receptor) in primary tumors were closely related to malignant prognosis. In addition, metastasis was induced by uPA in a cancer metastasis animal model and accordingly an uPA inhibitor could inhibit metastasis to some degree (Andreasen, P. A. et al., Int. J. Cancer 72(1):1-22, 1997). So, uPA seems to be a powerful and independent prognostic marker and at the same time be a potential target for the inhibition of invasion and metastasis (Andreasen P. A. et al., Int. J. Cancer 72(1):1-22, 1997). The cancer-related activities of other serine proteases have been comparatively less understood.
Recently, TTSP family (type II transmembrane serine protease family) has been newly identified as a serine protease family, which is over-expressed in prostatic carcinoma and ovarian cancer cells (Netzel-Arnett, S., et al., Cancer Metastasis Rev. 22(2-3):237-258, 2003). TMPRSS4 has been identified as a new member of type II TTSP family and confirmed to be expressed in pancreas cancer, large intestine cancer, and stomach cancer cells (Wallrapp, C., et al., Cancer Res. 15:60(10):2602-2606, 2000). TMPRSS4 is composed of 437 amino acids and its amino acid sequence is presumed to have trypsin-like activity. TMPRSS4 is bound to membrane by signal-anchor sequence of N-terminal and its extracellular region containing serine protease domain is glycosylated (Wallrapp, C., et al., Cancer Res. 15:60(10):2602-2606, 2000). It is also presumed that TMPRSS4 is involved in invasion and metastasis of pancreas cancer cells. However, a contradict result has been reported earlier saying that recombinant TMPRSS4 expression did not affect cancer invasion and progression in in vitro and in vivo pancreas cancer models (Wallrapp, C., et al., Cancer Res. 15:60(10):2602-2606, 2000). Thus, full explanations on the exact functions and systems of TMPRSS4 in relation to cancer cell growth, invasion and metastasis have not been given, yet.